Where is the scam?
These days, there are a number of companies willing to offer you a "Free Credit Report". Often times, there is a small fee that goes with these reports. It makes no sense to call it free if there is a fee.
Other sites require you to sign up for a membership to something or other. Your credit report is provided free, but you will receive an ongoing monthly charge. The charge is not actually for your credit report, it is just for being a part of their website.
The scam is simply that you do not have to pay anything to receive your credit report. As long as you only need it once a year, there is no fee.